Re: [PATCH v10 2/4] kbuild: generate offset range data for builtin modules

[Kris Van Hees]

On Sun, Sep 08, 2024 at 11:50:51AM +0900, Masahiro Yamada wrote:
> On Fri, Sep 6, 2024 at 11:45???PM Kris Van Hees <kris.van.hees@xxxxxxxxxx> wrote:
> >
> > Create file module.builtin.ranges that can be used to find where
> > built-in modules are located by their addresses. This will be useful for
> > tracing tools to find what functions are for various built-in modules.
> >
> > The offset range data for builtin modules is generated using:
> >  - modules.builtin: associates object files with module names
> >  - vmlinux.map: provides load order of sections and offset of first member
> >     per section
> >  - vmlinux.o.map: provides offset of object file content per section
> >  - .*.cmd: build cmd file with KBUILD_MODFILE
> >
> > The generated data will look like:
> >
> > .text 00000000-00000000 = _text
> > .text 0000baf0-0000cb10 amd_uncore
> > .text 0009bd10-0009c8e0 iosf_mbi
> > ...
> > .text 00b9f080-00ba011a intel_skl_int3472_discrete
> > .text 00ba0120-00ba03c0 intel_skl_int3472_discrete intel_skl_int3472_tps68470
> > .text 00ba03c0-00ba08d6 intel_skl_int3472_tps68470
> > ...
> > .data 00000000-00000000 = _sdata
> > .data 0000f020-0000f680 amd_uncore
> >
> > For each ELF section, it lists the offset of the first symbol.  This can
> > be used to determine the base address of the section at runtime.
> >
> > Next, it lists (in strict ascending order) offset ranges in that section
> > that cover the symbols of one or more builtin modules.  Multiple ranges
> > can apply to a single module, and ranges can be shared between modules.
> >
> > The CONFIG_BUILTIN_MODULE_RANGES option controls whether offset range data
> > is generated for kernel modules that are built into the kernel image.
> >
> > How it works:
> >
> >  1. The modules.builtin file is parsed to obtain a list of built-in
> >     module names and their associated object names (the .ko file that
> >     the module would be in if it were a loadable module, hereafter
> >     referred to as <kmodfile>).  This object name can be used to
> >     identify objects in the kernel compile because any C or assembler
> >     code that ends up into a built-in module will have the option
> >     -DKBUILD_MODFILE=<kmodfile> present in its build command, and those
> >     can be found in the .<obj>.cmd file in the kernel build tree.
> >
> >     If an object is part of multiple modules, they will all be listed
> >     in the KBUILD_MODFILE option argument.
> >
> >     This allows us to conclusively determine whether an object in the
> >     kernel build belong to any modules, and which.
> >
> >  2. The vmlinux.map is parsed next to determine the base address of each
> >     top level section so that all addresses into the section can be
> >     turned into offsets.  This makes it possible to handle sections
> >     getting loaded at different addresses at system boot.
> >
> >     We also determine an 'anchor' symbol at the beginning of each
> >     section to make it possible to calculate the true base address of
> >     a section at runtime (i.e. symbol address - symbol offset).
> >
> >     We collect start addresses of sections that are included in the top
> >     level section.  This is used when vmlinux is linked using vmlinux.o,
> >     because in that case, we need to look at the vmlinux.o linker map to
> >     know what object a symbol is found in.
> >
> >     And finally, we process each symbol that is listed in vmlinux.map
> >     (or vmlinux.o.map) based on the following structure:
> >
> >     vmlinux linked from vmlinux.a:
> >
> >       vmlinux.map:
> >         <top level section>
> >           <included section>  -- might be same as top level section)
> >             <object>          -- built-in association known
> >               <symbol>        -- belongs to module(s) object belongs to
> >               ...
> >
> >     vmlinux linked from vmlinux.o:
> >
> >       vmlinux.map:
> >         <top level section>
> >           <included section>  -- might be same as top level section)
> >             vmlinux.o         -- need to use vmlinux.o.map
> >               <symbol>        -- ignored
> >               ...
> >
> >       vmlinux.o.map:
> >         <section>
> >             <object>          -- built-in association known
> >               <symbol>        -- belongs to module(s) object belongs to
> >               ...
> >
> >  3. As sections, objects, and symbols are processed, offset ranges are
> >     constructed in a straight-forward way:
> >
> >       - If the symbol belongs to one or more built-in modules:
> >           - If we were working on the same module(s), extend the range
> >             to include this object
> >           - If we were working on another module(s), close that range,
> >             and start the new one
> >       - If the symbol does not belong to any built-in modules:
> >           - If we were working on a module(s) range, close that range
> >
> > Signed-off-by: Kris Van Hees <kris.van.hees@xxxxxxxxxx>
> > Reviewed-by: Nick Alcock <nick.alcock@xxxxxxxxxx>
> > Reviewed-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> > Reviewed-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
> > Tested-by: Sam James <sam@xxxxxxxxxx>
> > ---
> 
> 
> If v10 is the final version, I offer to locally squash the following:

Thanks!  That would be great!  v10 is indeed the final version (see bwlow).

> diff --git a/.gitignore b/.gitignore
> index c06a3ef6d6c6..625bf59ad845 100644
> --- a/.gitignore
> +++ b/.gitignore
> @@ -69,6 +69,7 @@ modules.order
>  /Module.markers
>  /modules.builtin
>  /modules.builtin.modinfo
> +/modules.builtin.ranges
>  /modules.nsdeps
> 
>  #
> diff --git a/Documentation/dontdiff b/Documentation/dontdiff
> index 3c399f132e2d..a867aea95c40 100644
> --- a/Documentation/dontdiff
> +++ b/Documentation/dontdiff
> @@ -180,6 +180,7 @@ modpost
>  modules-only.symvers
>  modules.builtin
>  modules.builtin.modinfo
> +modules.builtin.ranges
>  modules.nsdeps
>  modules.order
>  modversions.h*

> If Sami reports more errors and you end up with v11,
> please remember to fold it.

Sami confirmed v10 [0].  Can you squash his reviewed-by and tested-by as well?

Thanks for all the help!

	Kris

[0] https://lore.kernel.org/lkml/20240909191801.GA398180@xxxxxxxxxx/